Revert "Revert "Fully support pairs in the register allocator.""

This reverts commit c399fdc442db82dfda66e6c25518872ab0f1d24f.

Change-Id: I19f8215c4b98f2f0827e04bf7806c3ca439794e5
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 8d9a7b7..9665b0e 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -632,6 +632,14 @@
         break;
       }
 
+      case Location::kRegisterPair : {
+        stack_map_stream_.AddDexRegisterEntry(DexRegisterMap::kInRegister, location.low());
+        stack_map_stream_.AddDexRegisterEntry(DexRegisterMap::kInRegister, location.high());
+        ++i;
+        DCHECK_LT(i, environment_size);
+        break;
+      }
+
       default:
         LOG(FATAL) << "Unexpected kind " << location.GetKind();
     }